For example, the method described in Patent Document 1 is known as a polishing method of a magnetic head slider. A lapping oil composition for final polishing, for example, described in Patent Document 2 is known as a polishing solution for polishing the magnetic head slider.
Incidentally, the method described in Non-patent Document 1, for example, is known as a polishing method of a GaN substrate (gallium nitride substrate) instead of the magnetic head slider. This method is to polish the GaN substrate, using a diamond paste of the grain size of 0.1 μm and a pad of a suede type, and thereafter to chemically polish the GaN substrate, using a mixed solution of KOH and NaOH.
Another known polishing method of the GaN substrate is, for example, the method described in Patent Document 3. This method is to polish the GaN substrate by free abrasive grains supplied onto a platen. Specifically, while gradually decreasing the grain sizes of free abrasive grains, the GaN substrate is polished at decreasing polishing speeds.    Patent Document 1: Japanese Patent Application Laid-Open No. 2001-205556    Patent Document 2: Japanese Patent Application Laid-Open No. 2004-58220    Patent Document 3: Japanese Patent Application Laid-Open No. 2001-322899    Non-patent Document 1: J. L. Weyher and three others, “Chemical polishing of bulk and epitaxial GaN,” Journal of Crystal Growth, vol. 182, 1997, pp. 17-22.